The present invention relates to controllers for controlling a machine, a collection of devices on a production line or various types of industrial processes.
Industrial controllers are special purpose computers used for controlling industrial processes and manufacturing equipment on a real-time basis. These controllers include programmable logic controllers using ladder diagram programs and machine control I/O devices and process controllers using function chart symbolic language and complex analog/digital I/O or a combination of these.
Under the direction of a user-language application program, the industrial controller examines the state of inputs reflecting the state of the controlled process and sets the state of the outputs controlling the controlled process. During operation, those inputs and outputs can be graphically displayed using a human machine interface (HMI) in the form of process animation, logic ladder, data values, or similar construct to provide real-time or “live” monitoring of the industrial process. An operator, such as a process engineer, may then perform any diagnostic or debugging assessments on this “live” data.
Conventional HMI's are designed to process only real-time values that are received from the industrial controller processor. In order for a process engineer to assess the industrial process using the monitoring tools provided by the HMI, such as ladder logic and process animation, simulated data values for the industrial process must be created using a model of the industrial process and input to the HMI for processing. To debug the industrial process, or portion thereof, the process engineer must either debug a simulation of the industrial process or manually create values that are believed to be consistent with those provided during the industrial process. However, this modeled data may not reveal the problem with the actual industrial process which may deviate from the idealized model.
In contrast, historian services have been implemented in industrial control applications to acquire time-series data during cycles of the industrial process for retroactive analysis. Generally, historian services collect and store the data that is fed to the HMI. The data is stored in a database that arranges the data based on the time at which it was acquired. This time-ordered data thereby provides a historical perspective of the industrial process that can be used to generate trending reports, charts, graphs, and the like.
Industrial controller systems may be spread out in numerous devices such as controllers, HMIs, and intelligent actuators and sensors. The state of these I/O devices must be considered as well as the state of the central controller processor in determining the overall state of the controller. Errors in the operation of industrial controller systems can be caused by dynamic variables such as the speed of operation. Errors in the operation of industrial controller systems can also be intermittent and difficult to reproduce.
Capturing all of the I/O data associated with even a moderately complex industrial control system can be difficult or impractical both because of the large amount of data storage required and the necessary bandwidth of the data acquisition system needed to collect high resolution data samples with high precision.